1. Field of the Invention
The invention relates to a vulcanizable rubber mixture for fabricating an area of leather-hard rubber for a composite profile of leather-hard rubber/soft rubber, as well as to a vulcanizing process for such a mixture.
2. Description of the Prior Art
A composite profile known from German Petty Patent No. 7 510 829 is produced by joint extrusion and vulcanization of two different grades of rubber. This composite profile has an area of so-called "leather-hard rubber" and a second area, developed integrally therewith of ordinary soft, rubber-elastic rubber.
This "leather-hard rubber" represents a transition region between the ordinary soft rubber and the hard rubber and is generally considered "unusable". While its Shore-D-hardness is around 40 to 60 and, in particular, 50, and therefore corresponds to the hardness of hard rubber, its tensile strength is considerably lower than that of hard rubber and is approximately in the range of 50 to 250 kg per cm.sup.2. Its elongation is 30 to 60% and, in particular, about 35 to 40%.
This leather-hard rubber is therefore an elastically deformable material with relatively great hardness.
The advantage of such a composite profile is that the area of leather-hard rubber has approximately the same properties as sections of soft rubber customary heretofore, which were provided with steel reinforcement. This leather-hard rubber, therefore, furnishes relatively large clamping forces for fixing such a section.
While the soft rubber used for this composite profile can be produced from the customary mixtures, special mixtures are required for the leather-hard rubber, which mixtures lead to the desired properties of the area of leather-hard rubber and also can be extruded and vulcanized together with the soft rubber.
However, no rubber mixture known to date meets these requirements.